Production and characterization of thermo-, halo- and solvent-stable esterase from Bacillus mojavensis TH309

Synthesis of graphite/rGO-modified fungal hyphae for chromium (VI) bioremediation process

Bioremediation is a promising technology that can eliminate the drawbacks of conventional treatment methods in removing harmful toxic metals including chromium(VI). Therefore, in this study, fungal hyphae modified with graphite and reduced graphene oxide were synthesized and assessed for their potential to bioremediate heavy metals for the first time in the literature. The effects of the carbon-based materials on microbial structure were characterized using scanning electron microscopy analysis. Thermogravimetric, RAMAN, X-ray diffraction, and enzymatic analyzes were performed to determine the role of functional groups. In addition, batch adsorption experiments utilizing response surface methodology were conducted to optimize operating parameters such as time (1-11 h), chromium (10-50 mg/L), and graphite/reduced graphene oxide (0.1-1 g/L). The maximum adsorption capacity with the graphene fungal hyphae was determined to be 568 mg.g-1, which is 9.7 times that of the crude fungal hyphae. The Cr(VI) removal for fungal hyphae-graphite and fungal hyphae-reduced graphene oxide biocomposites was 98.25% and 98.49%, respectively. The isothermal and kinetic results perfectly matched the 2nd order pseudo-model and Langmuir model in terms of the nature of the adsorption process. The laboratory scale test results indicate that fungal hyphae modified with graphite and reduced graphene oxide have a high adsorption capacity, suitable for the removal of chromium (VI) from wastewater.

Heterologous expression, purification, and characterization of thermo- and alkali-tolerant laccase-like multicopper oxidase from Bacillus mojavensis TH309 and determination of its antibiotic removal potential

Laccases or laccase-like multicopper oxidases have great potential in bioremediation to oxidase phenolic or non-phenolic substrates. However, their inability to maintain stability in harsh environmental conditions and against non-substrate compounds is one of the main reasons for their limited use. The gene (mco) encoding multicopper oxidase from Bacillus mojavensis TH309 were cloned into pET14b( +), expressed in Escherichia coli, and purified as histidine tagged enzyme (BmLMCO). The molecular weight of the enzyme was about 60 kDa. The enzyme exhibited laccase-like activity toward 2,6-dimethoxyphenol (2,6-DMP), syringaldazine (SGZ), and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The highest enzyme activity was recorded at 80 °C and pH 8. BmLMCO showed a half-life of ~ 305, 99, 50, 46, 36, and 20 min at 40, 50, 60, 70, 80, and 90 °C, respectively. It retained more than 60% of its activity after pre-incubation in the range of pH 5-12 for 60 min. The enzyme activity significantly increased in the presence of 1 mM of Cu2+. Moreover, BmLMCO tolerated various chemicals and showed excellent compatibility with organic solvents. The Michaelis constant (Km) and the maximum velocity (Vmax) values of BmLMCO were 0.98 mM and 93.45 µmol/min, respectively, with 2,6-DMP as the substrate. BmLMCO reduced the antibacterial activity of cefprozil, gentamycin, and erythromycin by 72.3 ± 1.5%, 79.6 ± 6.4%, and 19.7 ± 4.1%, respectively. This is the first revealing shows the recombinant production of laccase-like multicopper oxidase from any B. mojavensis strains, its biochemical properties, and potential for use in bioremediation.

Heterologous expression, molecular studies and biochemical characterization of a novel alkaline esterase gene from Bacillus thuringiensis for detergent industry

Present study was aimed to clone and express the esterase encoding gene from Bacillus thuringiensis in E. coli BL21. Purification of recombinant esterase enzyme was achieved up to 48.6 purification folds by ion exchange chromatography with specific activity of 126.36 U mg^-1. Molecular weight of esterase enzyme was 29 kDa as measured by SDS-PAGE. Purified esterase enzyme showed stability up to 90% at 90 °C and remained stable in a wide pH range (8-11). Molecular docking strengthens the experimental results by showing the higher binding energy with p-NP-butyrate. Enzyme activity was found to be reduced by EDTA but enhanced in the presence of other metal ions. Enzyme activity was reduced with 1% SDS, PMSF, and urea but organic solvents did not show considerable impact on it even at higher concentrations. Purified recombinant esterase was also found to be compatible with commercial laundry detergents and showed very good stability (up to 90%). All these properties proved the esterase enzyme from B. thuringensis a significant addition in detergent industry.

Bacillales: From Taxonomy to Biotechnological and Industrial Perspectives

For a long time, the genus Bacillus has been known and considered among the most applicable genera in several fields. Recent taxonomical developments resulted in the identification of more species in Bacillus-related genera, particularly in the order Bacillales (earlier heterotypic synonym: Caryophanales), with potential application for biotechnological and industrial purposes such as biofuels, bioactive agents, biopolymers, and enzymes. Therefore, a thorough understanding of the taxonomy, growth requirements and physiology, genomics, and metabolic pathways in the highly diverse bacterial order, Bacillales, will facilitate a more robust designing and sustainable production of strain lines relevant to a circular economy. This paper is focused principally on less-known genera and their potential in the order Bacillales for promising applications in the industry and addresses the taxonomical complexities of this order. Moreover, it emphasizes the biotechnological usage of some engineered strains of the order Bacillales. The elucidation of novel taxa, their metabolic pathways, and growth conditions would make it possible to drive industrial processes toward an upgraded functionality based on the microbial nature.

An Esterase with Increased Acetone Tolerance from Bacillus subtilis E9 over Expressed in E. coli BL21 Using pTac Bs-est Vector

Bacillus subtilis E9 was identified as a potential strain producing esterase. The gene coding esterase from B. subtilis E9 was amplified using esterase-specific primers and the sequence was translated in silico. The presence of conserved catalytic triad amino acid residues (His-Ser-Asp/Glu) confirmed the functional nature of the esterase enzyme. Docking studies conducted with modeled protein and the ligand p-nitrophenyl acetate showed that the amino acid residues interacting with the ligand were Ser77, His76, and Gly103. The gene coding for esterase from B. subtilis E9 was cloned into an assembled vector having Tac promoter (pTac), pUC origin of replication, Ni-Histidine residues, ampicillin cassette, and T7 terminator using Golden gate DNA assembly method. The generated pTac Bs-est (4598 bp) recombinant plasmid was transformed and heterologously expressed in Escherichia coli BL21 (DE3) strain. The tagged recombinant protein was purified to yield 43.4% pure protein with specific activity of 772 U/mg. The purified recombinant protein was subjected to peptide sequencing and the identity was confirmed as esterase by peptide tandem mass fragmentation method using the LC-MS/MS analysis. The purified recombinant esterase was found to be organic solvent stable and tolerant up to 5 days retaining around 95% residual activity in 30-90% v/v Acetone. The recombinant esterase expressed in our study was found to exhibit better organic solvent stability and tolerance than compared to the original bacterial esterase from B. subtilis E9, a property which could be explored in the biocatalytic and synthetic transformation reactions for industrial applications.

A novel biodemulsifier of Bacillus mojavensis XH1 - Oxalate decarboxylase with the potential for demulsification of oilfield emulsion

In recent years, special attention has been devoted to biodemulsifiers as a new type of environment-friendly demulsifiers. A novel biodemulsifying oxalate decarboxylase (OxdC) secreted by Bacillus mojavensis XH1 is reported in the present study. A genome-wide comparison showed that strains with high demulsification efficiencies all possess alkane degradation genes. An analysis of the differentially expressed genes and proteins induced by different substrates showed that OxdC secreted by XH1 was an effective demulsifier. Moreover, the demulsification ability was verified by prokaryotic gene expression, knockout and complementation analyses. OxdC from XH1 exhibited a strong demulsification capacity and significantly outperformed the model protein Bacillus subtilis 168 OxdC (Yvrk), which shared a high amino acid similarity but showed limited demulsification ability. Based on a comparison of the structural characteristics, the hydrophobic amino acids on the surface of OxdC were identified as a key factor driving the favorable demulsification activity of XH1. The metabolic pathways of XH1 used liquid paraffin and glucose as substrates, illustrating that hydrocarbons are necessary for biodemulsifier secretion. The present study provides new insight into the application of OxdC as an additional genetic resource in biodemulsification.

A Novel Carboxylesterase Derived from a Compost Metagenome Exhibiting High Stability and Activity towards High Salinity

Halotolerant lipolytic enzymes have gained growing interest, due to potential applications under harsh conditions, such as hypersalinity and presence of organic solvents. In this study, a lipolytic gene, est56, encoding 287 amino acids was identified by functional screening of a compost metagenome. Subsequently, the gene was heterologously expressed, and the recombinant protein (Est56) was purified and characterized. Est56 is a mesophilic (T_opt 50 °C) and moderate alkaliphilic (pH_opt 8) enzyme, showing high thermostability at 30 and 40 °C. Strikingly, Est56 is halotolerant as it exhibited high activity and stability in the presence of up to 4 M NaCl or KCl. Est56 also displayed enhanced stability against high temperatures (50 and 60 °C) and urea (2, 4, and 6 M) in the presence of NaCl. In addition, the recently reported halotolerant lipolytic enzymes were summarized. Phylogenetic analysis grouped these enzymes into 13 lipolytic protein families. The majority (45%) including Est56 belonged to family IV. To explore the haloadaptation of halotolerant enzymes, the amino acid composition between halotolerant and halophilic enzymes was statistically compared. The most distinctive feature of halophilic from non-halophilic enzymes are the higher content of acidic residues (Asp and Glu), and a lower content of lysine, aliphatic hydrophobic (Leu, Met and Ile) and polar (Asn) residues. The amino acid composition and 3-D structure analysis suggested that the high content of acidic residues (Asp and Glu, 12.2%) and low content of lysine residues (0.7%), as well as the excess of surface-exposed acidic residues might be responsible for the haloadaptation of Est56.

Evaluation of biomass pretreatment to optimize process factors for different organic acids via Box-Behnken RSM method

Biomass, as renewable energy source, is of importance to investigate to extend the conversion yield by microorganism. Because of lignocellulosic structure, biomass must be pretreated with a process, frequently inorganic acid has to be used with a problem of hazardous byproducts. Organic acid pretreatment is an efficient alternative to be investigated. Sugar beet pulp, as an agro-industrial residue of microorganism, can be utilized by pretreatment, which is usually a costly process. Pretreatment with organic acids creates a great opportunity to convert the process into more economic and effective. Moreover, pressure conditions significantly increase the yield of biodegradable sugar content. In this study, different organic acids of maleic, fumaric, oxalic, and acetic acid pretreatment was investigated to pretreatment of sugar beet pulp, which came vast amount from factories, under pressure and non-pressure conditions via Box-Behnken method to estimate optimum point of acid ratio (1, 3, 5%), time (10, 27.5, 45 min), and solid ratio factors (3, 6.5, 10%) for highest degradation. Results were also evaluated economically. As a result of the experiments, it was observed that acetic acid gave the best result with 409.16 g/L total sugar concentration than the other organic acids. The highest TS concentration of maleic, oxalic, and fumaric acid were 97.26, 97.85, and 91.37 g/L, respectively, under pressure. According to economical evaluation, owing to lower market price and highest TS formation yield, pretreatment cost of acetic acid pretreatment was found averagely 1.51 $/gTS under pressure conditions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10163-021-01276-7.

Revisiting the scope and applications of food enzymes from extremophiles

Microorganisms from extreme environments tend to undergo various adaptations due to environmental conditions such as extreme pH, temperature, salinity, heavy metals, and solvents. Thus, they produce enzymes with unique properties and high specificity, making them useful industrially, particularly in the food industries. Despite these enzymes' remarkable properties, only a few instances can be reported for actual exploitation in the food industry. This review's objectives are to highlight the properties of these enzymes and their prospects in the food industry. First, an introduction to extremophilic organisms is presented, followed by the categories and application of food enzymes from extremophiles. Then, the unique structural features of extremozymes are shown. This review also covers the prospective applications of extremozymes in the food industry in a broader sense, including degradation of toxins, deconstruction of polymers into monomers, and catalysis of multistep processes. Finally, the challenges in bioprocessing of extremozymes and applications in food are presented. PRACTICAL APPLICATIONS: Enzymes are important players in food processing and preservation. Extremozymes, by their nature, are ideal for a broad range of food processing applications, particularly those that require process conditions of extreme pH, temperature, and salinity. As the global food industry grows, so too will grow the need to research and develop food products that are diverse, safe, healthy, and nutritious. There is also the need to produce food in a sustainable way that generates less waste or maximizes waste valorization. We anticipate that extremozymes can meet some of the research and development needs of the food industry.